I always loved these arcs to display progress, but the only way to create them is using JavaScript and a canvas or simply images.
But with the new awesome CSS3 techniques it is finally possible to create them with pure CSS.

So this is how a pure CSS3 arc looks like (try a hover)

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35%

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This works best in Chrome, but also in Firefox and OperaIE is not supported – Who would have thought?

Chrome has this great feature to use gradients as a mask. Thats how the inset around the circle is created (FF and Opera only show a white border)